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Abstract

We investigate dierent methods for estimating anthropogenic CO2 using modelled continuous atmospheric concentrations of CO2 alone, as well as CO2 in combination with the surrogate tracers CO, 13C(CO2) and É14C(CO2). These methods are ap- 5 plied at three hypothetical stations representing rural, urban and polluted conditions. We find that independent of the tracer used, an observation-based estimate of continuous anthropogenic CO2 is not feasible at rural measurement sites due to the low signal to noise ratio of anthropogenic CO2 estimates at such settings. At urban and polluted sites, potential future continuous É14C(CO2) measurements with a precision 10 of 5‰ or better are most promising for anthropogenic CO2 determination (precision ca. 10–20 %), but the insensitivity against CO2 contributions from biofuel emissions may reduce its accuracy in the future. Other tracers, such as 13C(CO2) and CO could provide an accurate and already available alternative if all CO2 sources in the catchment area are well characterized with respect to their isotopic signature and CO to 15 anthropogenic CO2 ratio. We suggest a strategy for calibrating these source characteristics on an annual basis using precise É14C(CO2) measurements on grab samples. The precision of anthropogenic CO2 determination using 13C(CO2) is largely determined by the measurement precision of 13C(CO2) and CO2. The precision when using the CO-method is mainly limited by the variation of natural CO sources and CO 20 sinks. At present, continuous anthropogenic CO2 could be determined using the tracers 13C(CO2) and/or CO with a precision of about 30 %, a mean bias of about 10% and without significant diurnal discrepancies. This allows significant improvement, validation and bias reduction of highly resolved emission inventories using atmospheric observation and regional modelling.